The disinfection of water by ultraviolet radiation has been know for decades. Ultraviolet radiation disinfects both effluent and drinking water by damaging the DNA of pathogenic microorganisms, which comprises their ability to multiply and consequently prevents infections.
Whereas effluent is conventionally irradiated in the context of water treatment plants in open tanks or unpressurised pipe systems, in the field of drinking water and for disinfecting media with reduced UV transparency it is conventional to use closed stainless steel channels with UV radiators arranged in them. The irradiation space in these channels is also referred to as a reactor.
For effective disinfection of pathogenic germs in drinking water, it is necessary for every microorganism contained in the water to receive a particular minimum dose of ultraviolet radiation. The dose is equal to the irradiation intensity multiplied by the irradiation time. Conventional reactors have an inlet and an outlet, which are arranged at the ends of the reactor in the flow direction and are aligned in a radial direction. They feel the medium directly into the irradiation space. The medium to be irradiated is guided through the reactor either in an approximately U-shaped or Z-shaped direction, depending on the alignment of the connections. With this arrangement, it has been found that preferred flow paths are formed. In these flow paths, the water with the microorganisms contained in its is delivered particularly rapidly through the reactor. The speed in this region entails a short residence time, which necessitates a relatively high radiation intensity for a good disinfection result. Other flow paths, in which the flow rate is lower, receive a substantially higher radiation dose than is actually necessary, owing to the rather homogeneous radiation distribution inside the reactor. The radiation is therefore not utilized optimally.
U.S. Pat. No. 4,296,066 discloses a reactor in which a single UV radiator is surrounded by a coaxial glass tube and, further outwards, by a coaxial influx chamber. The water to be irradiated firstly enters the influx chamber and passes externally around the glass tube into an open end. In this way, the microorganisms in the flowing water received a first radiation dose which passes through the coaxial inner tube. The flow then enters the inner tube at an open end, and passes through between the inner tube and the radiator, before emerging at the other end of the inner tube. On the second sub-path between the radiator and the coaxial inner tube, the microorganisms contained in the water received a second, significantly higher radiation dose. The total dose which is relevant to the disinfection in the sum of the two doses, i.e. the first dose received in the outer space and the dose subsequently received in the inner space. Owing to the coaxial arrangement of the inner tube and the radiator and the relatively narrow annular gap between these two components, it is not likely that zones with a particularly low flow rate will form. The reactor according to U.S. Pat. No. 4,296,066, however, is elaborately designed and suitable only for a single UV radiator.